The working device part of an electric forkhoist truck generally includes a battery, a controller, a frequency conversion driving module, an electric motor of a frequency control asynchronous alternating-current pump, a hydraulic pump, a control valve and a hydraulic actuating part. Now, taking the hoisting and lowering of the cargo as an example, the working process thereof will be described below: 1, when implementing the hoisting operation of the cargo, the main process thereof includes: operating a hoisting piece handle (3) of a multi-way valve (4)→signaling by a hoisting electric of the multi-way valve (4)→sensing, by a controller of a converter (21), an incoming signal of an intelligent display (19), and starting an electric motor (16) via a frequency conversion driving module→driving a hydraulic pump (7) to output pressure oil through the electric motor (16)→inputting the pressure oil into a P1 port and an A1 port of the hoisting piece of the multi-way valve (4) via an EF pipeline of a steering priority valve (8)→a governor valve (17)→a hoisting cylinder (9)→hoisting the cargo; 2, when unloading the cargo from the height, the main process thereof includes: operating the hoisting piece handle (3) of the multi-way valve (4)→communicating the T1 port with the A1 port of the hoisting piece of the multi-way valve (4)→the pressure oil in the hoisting cylinder passing through the governor valve (17), the A1 port and T1 port of the multi-way valve, and a filter (10), and then flowing into a tank (5)→the cargo lowering from the height with a certain speed, at the moment, the pump electric motor will not be started if no other action operations are carried out synchronously. From the above operations, it can be seen that, when the cargo with certain height and weight is unloaded from the height, the potential energy of the cargo is totally dissipated by converting to be heat.